The Savill Gardens Gridshell, Glen Howells Architects

All photo’s (except where otherwise stated) courtesy of Glenn Howells Architects

In the late nineteen eighties the German engineer-architect, Frei Otto, visited Dorset in South West England. Otto had been invited by the furniture maker and entrepreneur, John Makepeace, to participate in a wood build experiment which aimed to revitalise the use of roundwood thinnings, or wastewood. The result was the main furniture and crafts workshop at Hooke Park, the forest-based teaching and learning addition to Makepeace’s Parnham House Furniture School, down the road in the small and picturesque village of Beaminster. It was, as it turned out, Otto’s only project in this country.

Back in Germany, Otto’s reputation remains formidable to this day. Some of this has to do with Munich’s 1972 Olympic stadium, which he designed and which is still, apparently, many a German citizen’s favourite piece of modern architecture. Among the wood architectural fraternity he is best known, however, for the Mannheim Multihall, an extraordinary organic labyrinth of curving timber lattices, combining a series of pod-like snake-skin walk-through entrances and exits, and encompassing two open space halls. The building was originally designed as a temporary structure for a flower festival.  The structural engineering technique Otto developed for Mannheim he called gridshells. Again, despite its success, Mannheim is the only gridshell Otto actually completed.

Frei Otto’s Mannheim Multihall 33 years on in 2007 (photo: Oliver Lowenstein Fourth Door Research)

A major and, at the time, insurmountable problem to building further gridshells was  breakages among the laths, the long strips of wood which criss-crossed to comprise the double curvature gridshell skin. Back then, there seemed to be no way around this. Although the engineering for Mannheim was very advanced for the time, optimising the geometry to reduce breakages was very difficult, and reportedly the lath breakages for Mannheim were over 11, 000. Many of the mathematical calculations for Mannheim were done, in that pre-computer age, by some of the smartest engineering brains of the generation, including the English engineers, Ian Liddell and Ted Happold. The two had for many years worked at the international, though London centred, firm of engineers, Ove Arup. However, in 1972 they went independent and set up the firm of Buro Happold, with Happold continuing as prime engineer at Otto’s court. Liddell and Happold worked on many Frei Otto projects together, including a variety of wood projects, of which Mannheim was but one,  though  the most ambitious.

It was Buro Happold who provided all the engineering for Otto’s, and the other subsequent, Hooke Park buildings designed in collaboration with Edward Cullinan Architects, and the experience of Mannheim stayed in their minds. The centrality of sustainability at Hooke Park has been disputed, but what Hooke Park did do is show that waste round wood could be used for building, and the buildings have remained an inspiration for each subsequent generation of timber-hued architects.

The Weald & Downland Open Air Museum gridshell by Edward Cullinan Architects shortly after opening (Photo Stewart )

Happold, in fact, were keen to build a gridshell at Hooke Park, but this proved impracticable. Their chance to build a gridshell came soon enough, however, when Cullinan’s and Happold, were appointed to design the Weald and Downland Museum Gridshell in the later nineties. What had changed in the intervening years was the arrival of computer technology, including the ability to model the physics and geometry of shell-structures to minimise breakages. At the Weald and Downland build this added dimension reduced breakages radically, making the gridshell technique far more feasible to realise. The Weald and Downland Gridshell, as many will know, has been very successful, winning awards, and becoming something of an icon for one possible future to timberbuild. This is  not surprising;  it is a beautiful and resolved building. In the years since there has been a significant and definite undertow of fascination for the gridshell form among many in the architectural world, with a steady flow of plans for new gridshells emerging from computer screens and drawing boards around the country, but none, frustratingly, have as yet to be built.

This summer all that changed, with the opening of the first major gridshell since Weald and Downland five years ago. The Savill Building, the ticketing and visitor gateway to Savill Gardens in Great Windsor Park, redefines the gridshell, pulling its design far from its experimental beginnings and into the mainstream. And yet quite a bit of the ancestry of those previous buildings – from Mannheim through Hooke Park, to the Weald and Downland building – is very much part of this brand new, ambitious and thoroughly modern gridshell at Savill Gardens. Buro Happold are in there again, as are the Weald and Downland carpenters, – Green Oak Carpentry Company, – although this time they have teamed up with the Glenn Howells Practice. Thirty years on, the Otto timberbuild spirit is in the air again.

Savill Gardens is part of the Royal Family’s land, managed by the Crown Estates, and set within Great Windsor Park. Although unlikely, given the Royals staid and conservative reputation, the Estate have plumped for a wholly avant-garde building, a kind of evidence that even the ultimate bastions of the establishment need to move with the times. The decision to build a gridshell by Crown Estates highlights the paradoxes of a defining conservative organisation finding iconic architecture mandatory for raising profile and profit. “We wanted, shall we say, a contemporary building,” states the diplomatic Estates ranger, Derek Rogers, at the press launch in June, going on to detail how the limited competition for Savill Gardens stipulated both an eye-catching building, and timber as a core material harvested from Windsor Great Park” s own sustainably managed woodland.

Approaching the building from the Gardens car-park entrance, only the hint of the full gridshell is visible, behind an earth covered and landscaped entrance corridor. The curvature of the three valleyed larch grid deck is much flatter than either Mannheim or Weald and Downland, apparently the lowest curvature manageable, in order, says architect Glenn Howells, so as not to break the tree-line. From outside, the deck is just as organic as its forebears, but by comparison, a slim futuristic, leaf-like shape gives a slick contemporary feel. And at 90 by 25 metres the Savill Building is the first gridshell to compete with Mannheim scale-wise, and is twice the size of the Cullinan building. Once inside the canopy becomes clear – at least if you look up “with the criss-crossing larch laths coming into their own, playing perceptual tricks within the troughs and domes. Compared to the timber experimentalism of its predecessors, however, Glenn Howells have fused the deck with mainstream materials, including two tone brick along the interior wall of the entrances – ticketing area; steel struts; a further steel rim edge tube holding the grid; and an extensive curtain of window paneling for viewing the beginnings of the gardens.

There are other differences, as well. The actual gridded shell doesn’t make it to the ground. On the entrance side, the roof structure begins within the softly sloping, grass covered, earth wall, within which are a group of rooms, for ticketing, etc, before entering the restaurant and shop facilities which sit on oak flooring under the canopy. On the gardens entrance, or far side the steel pylon quadropod struts hold the long tubular steel edge beam, which then connects to the far edge of the grids’ roof. This edge beam holds much of the roof load, and the deck ends in an overhang, rather than dropping to the ground.  The quadropod steel struts, developed separately by the small engineering practice, Haskins, Robinson, and Waters, – (HRW) who also worked on the concrete building, – take most of the shells’ load. Much engineering effort went into designing the connectors between that edge beam and the lath system of latticed shell.

From inside, the view out is to the beginnings of the park.  Between the end of the gridshell  and the ground is the glazing system, the glass panels enclosing this visitor area with windows between 8.5 to 5 metres in height, providing a degree of protection along with a dramatic first view of the gardens’ entry paths  for those just arriving.

For Andrew Holloway, managing director of Green Oak Carpentry, the Savill Gardens building is a distinctive contrast to the Weald & Downland gridshell. “It’s a very different approach to the whole aesthetic of Cullinan’s gridshell. Cullinan’s approach was to use materials honestly and let the building speak for itself. In a sense that’s a ‘warts and all’ approach to construction, where you make the detailing work as elegantly as you can and the buildings’ structural aspects become part of the story. In this it’s concealed; the architects are much more interested in clean, simple, elegant, uncluttered lines, so that the buildings’ working parts are hidden. That’s really okay.”

Photo Oliver Lowenstein, Fourth Door Research

In the evolution of the gridshell, Holloway believes the hybrid nature of the structure, with its edge beam steel legs, represents its most innovative element. “It is a very interesting further application and development of shell structures”, says Holloway. ˜The evolutionary process that this building represents moves shell structures into what is the most difficult structural form, which is roof only, shell only curvature retained by a perimeter beam which is propped off the ground. That is the significant achievement of the building in construction terms.”

Despite the palette of modernist materials, the semi-medieval practice of resorting to real trees in the building process couldn’t be avoided, with oak and larch sourced from Windsor Great Park. Green Oak advised on which trees were to be used, and means of  procurement though the wood needed to be cut some distance away as the Windsor Park sawmill had closed a decade earlier.

In addition, the timber, once cut, was sent to In Wood, the Sussex based company who have made a speciality out of preparing 6 m finger and scarf jointed laths. These were then returned to the site, where Green Oak had set up a poly-tunnel workshop where the sections were glue screwed into the long lath lengths for the roof.

The diagonal laths are 46 metres in length, 12 metres longer than ones comparable for Weald & Downland, for whom this kind of work was first done. Here, however, the wood is doubled using two laths to make up a length of almost 100 metres for the buildings’ length. Beginning with eight carpenters in February 2005, the number increased to eighteen at the busiest times. The building was also lowered with the same Peri scaffolding system used at Weald and Downland. What differed here was that the scaffolding’s lowering element was independent of the support scaffold, making adjustment much easier. Another fundamental difference was that at Weald and Downland all three of the shells’ layers were on before the lowering began, while here the lowering was done with only two layers; the first double layer of laths, followed by the second individual
layer. This has meant that one of main design innovations at Weald and Downland, the node clamp systems, became unnecessary. The nodes have been replaced by bolts’ bolted through layers separately, one through the upper, and one through the lower grid, assisted to by shear blocks, which, in effect join the two grids together, making them act as a beam.

Although the steel edge beam system has been used, a timber edge beam system was considered but would have been large and chunky, about 1.2 metres deep. Given the thin clean edges of the architectural concept such thick wooden legs felt intuitively alien, and were dropped.

Also in the early design process, the intention was to make the building;  a full shell structure running down to the ground. In this version the shell structure ended with legs down to the ground, which were to be formed from big glue-laminated timber legs landing on steel struts, in turn bolted to the substructure. Too complicated and too expensive, the steel props consequently became the key design solution.

The low angle of the buildings’ orientation is intended to make the most of solar gain, so that the building doesn’t require cooling. Heated by a lower energy gas fired system, the shell overhang on the Garden side’s window curtain also encourages natural ventilation. Although the gridshell canopy is its primary feature, followed by the locally sourced timber, as well as Kerto cladding, Savill Gardens ticks various other current low energy boxes. However, it would be hard to describe as a thorough-going example of a sustainable building, and indeed, this was never the main part of the brief.

Nonetheless, the Savill building pulls gridshells further into ‘iconic building’territory. Its mix of slick modernist design and modernist materials may well auger a rather different future for both design and technique, to the modern medieval dreamings generated by the line of buildings that came before it. As one sardonic wag noted, that there’ll probably be gridshell kits in IKEA within a few years. And, again, it does provide both an impressive exemplar of what contemporary timberbuild can deliver, along with a significant new pool of research, skill and knowledge as well as experience, which can  be called upon to develop further, more thoroughly and truly sustainable gridshell structures. Whether in Savill Gardens, making and building any perceived alternative identity the gridshell may have had, has been lost for good, is too early to tell for sure. The hope must be that this new timber showcase will inspire and motivate the design of a next generation of gridshells and other shell structure buildings over the coming years.

A version of this piece was first published in Building For A Future Vol 16, Winter 2006/7

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